In the use of various cable systems involving cables, it is desirable to provide a self adjustment device for automatically adjusting and maintaining tension on the cables.
Prior methods of maintaining tension on cable controls have employed in line springs with no variation of mechanical advantage such as the mechanism seen in U.S. Pat No. 4,344,518. These mechanisms have been used to applying tension to a cable control through the inner member, the conduit and between the inner member and conduit.
There are two disadvantages of such prior art. The prior systems do not apply a constant force and consequently have a shorter adjustment length for their size. These systems employ a constant displacement ratio of spring movement to system movement. This causes the load applied to the system by the spring to diminish linearly with spring travel. If a small tolerance of system tension is required, the prior art of tensioning can only be used effectively for an equally small amount of travel.
The prior devices cause the system to be larger and heavier. Mechanical disadvantages of the spring force is not used. This makes the spring required for a given amount of travel in the tolerance limits larger than would be needed in a system using a mechanical disadvantage.
Among the objectives of the present invention are to provide a self adjusting cable control device that will provide a constant force on the cables, which is small, which is less expensive, and which provides a higher spring constant for the volume of the device.
In accordance with the invention, a constant force self adjusting cable control device comprising a first member and a second member pivoted to one another about a pivot point, a tension spring connected to the first and second members and yieldingly urging the first and second members in a direction to cause movement about the pivot point and a cable attached to each of the first and second members. The cables are axially aligned such that the axis of the tension spring and the axis of the cables are parallel. The angular displacement between the points of attachment of the spring and the cable on one member forms an angle equal to the angle of the point of attachment of the spring and the cable of the other member whereby substantially constant tension is provided on each of the cables. The device further includes a one-way latch which automatically releases when there is any slack in the cables thereby permitting relative movement between the two members until the tension on the cables is re-established.